1. Field of the Invention
This invention relates to an electronic clinical thermometer and, more particularly, to an electronic clinical thermometer which includes an arithmetic unit for measuring the temperature of a part of the human body and for producing a signal indicative of the measured value, display means for presenting a visible display of the measured value, and an envelope for accommodating the arithmetic measurement unit and the display means. The thermometer is so adapted that the displayed value can be easily read even in a dark location.
2. Description of the Prior Art
The display unit in an electronic clinical thermometer of the above-described type most generally employs a highly reliable liquid crystal display element which consumes very little electric power. The progress that has been made in electronic techniques, moreover, has facilitated the development of such electronic clinical thermometers of small size. Because the liquid crystal display element presents a visual image by utilizing a difference in the reflectance of light, visual recognition of the displayed information is not possible unless there is a certain degree of external light available. This requires the provision of illuminating means so that the display can be read in the dark. In consideration of the fact that electronic clinical thermometers are frequently used in the dim light of morning and evening in, e.g., hospitals, it has been proposed that a light-emitting diode be employed as the display element. A light-emitting diode, however, consumes far more electric power than a liquid crystal display element and is unsuitable for use in small-sized electronic clinical thermometers which, relying upon a battery as the power source, do not provide enough space for the installation of a battery of large capacity.
For the arrangement having the liquid crystal display and illuminating means such as a lamp, it has been proposed that the electronic clinical thermometer be provided with a manual switch actuated by the operator to illuminate the display unit when necessary. Providing the switch, however, necessitates the use of many mechanically movable parts such as a manually operated push-button and mechanical contacts. Numerous problems arise in attempting to employ such a switch in a small size electronic clinical thermometer wherein a probe and display unit are integrated into a single package. Primarily, since a push-button forms a projection which protrudes from the thermometer envelope, the button is likely to be pressed accidentally by being inadvertently contacted by the operator's body when the thermometer is used. Also, when the thermometer is to be made small in size, it is required that the mechanical contacts used in the switch be comparatively small. Owing to wear with long use as well as insufficient mechanical strength, such contacts tend to lose their ability to make good contact and, hence, diminish the reliability of the electronic clinical thermometer as a whole. Furthermore, the fact that mechanically movable parts are provided which are operative from outside the thermometer makes it difficult to maintain the liquid tightness of the thermometer. This can limit the lifetime of the thermometer severely when one considers that a clinical thermometer must often be washed and sterilized with water or disinfectants.